Impact drill



Aug. 2, 1955 y R. E. sNYDER IMPACT DRILL 2 Sheets-Sheet l Original FiledMarch l5.I 1947 @oaf/W5 5M/r0.5@

INVENTOR.

BY Afro/aven Aug 2, 1955 R. E. SNYDER 2,714,500

IMPACT DRILL Original Filed March l5, `194'? V2 Sheets-Sheet 2 rrppN-KUnited States Patent O IIVIPACT DRILL 734,990, March applicationFebruary 6, 1952, Serial Continuation of application Serial No.

15, 1947. This No. 270,189

6 Claims. (Cl. Z55- 3) My invention relates generally to impact drills,and more particularly to impact drills of the type in which a hammermember is reciprocably mounted on a shank, and is caused to impactagainst an anvil or other suitable means to thereby deliver a series ofimpacts to the bit. This application is a continuation of my co-pendingapplication Serial No. 734,990, filed March 15, 1947, now abandoned.

In the drilling of wells, such as oil Wells, it has been found that thespeed and general eflciency of the drilling operations may be greatlyimproved by the use of a drill in which the rotating bit periodicallyhas impacts transmitted to it to force it into the formation beingdrilled. In my co-pending applications for Impact Drills, No. 527,179,filed March 20, 1944, now Patent No. 2,425,012, issued August 5, 1947;No. 674,526, tiled June 5, 1946, now abandoned, and No. 714,339, tiledDecember 5, 1946, now Patent No. 2,635,852 issued April 2l, 1953, I havedisclosed new and improved types of rotary impact drills which areoperated in this manner. Broadly, each of these drills is operated by abody which is rotatably mounted upon a rotary drill stem, and which isprovided with Huid-engaging means so that relative rotation occursbetween the body and the shank. The relative rotation is then used tooperate driving means, such as cam means, to reciprocate the hammer. Ingeneral, the Huidengaging means of my previous drills have comprisedradially extending blades or vanes having a substantial surface areawhich acts against the fluid in the hole when the drill is rotated aboutits longitudinal axis. When the blades are formed of a rigid materialsuch as metal, there may be a tendency for the drill to hang up ifprojections are left in the wall of the well. Furthermore, with a rigidblade the same amount of blade surface is presented to the uid at alltimes regardless of the speed of the hammer body, and consequently thetorque devel oped by the latter increases rapidly as the speed ofrotation is raised. While this latter feature is under certaincircumstances desirable, it is sometimes preferable to have the torquedeveloped by the body and blades remain fairly constant as therotational speed of the body is varied widely, and this may be done bydesigning the blade to yield under load. At all times it is desirablethat the drill not hang up in the well, and hence any construction whichreduces the possibility of this is quite desirable.

It is therefore a major object of this invention to provide an impactdrill of the above-mentioned type which is provided with resilientfluid-engaging means which will pass over obstructions of the typesometimes encountered in wells, without jamming or hanging up thereon.

Another object of my invention is to provide such a uid drag body havingblades which develop a torque varying within a narrow range as therotational speed of the bady is changed between Wide limits.

It is a further object of my invention to provide a body of this typehaving blades which may be adapted to spread mud or similar materialuniformly over the surface of the well wall with a troweling action tothereby smooth and seal the wall.

Still another object of my invention is to provide a resilient bladeconstruction in which the damaging or injuring of one blade section doesnot necessarily weaken or damage the remainder of the sections.

It is a still further object of my invention to provide a bladestructure which is economical to manufacture and which is designed towithstand the abuse and mistreatment it will normally receive in theeld, while still being quickly and easily replaceable should any damageoccur.

These and other objects and advantages of my invention will becomeapparent from the following description of preferred and optional formsthereof, and from the drawings illustrating those forms in which:

Fig. l is a side elevational View of a drill constructed in accordancewith my invention and installed in a well, a portion of the structurebeing broken away to show the details of construction;

Fig. 2 is a cross-sectional ure l;

Fig. 3 is a cross sectional view of one of the blade sections shown inFig. 2, but enlarged to show its details of construction;

Fig. 4 is a fragmentary vertical View, similar to Fig. l, of theretarder body having a series of helically extending blades; i

Fig. 5 is an optional method of constructing the resilient bladesections;

Fig. 6 is a view similar to Fig. `2, showing the method of attaching theblades shown in Fig. 5;

Fig. 7 shows one method of providing a continuous reinforcing core forblade sections;

Fig. 8 is a side elevational view, similar to Fig. l, of a form of mydevice adapted to wipe the wall of the hole and spread mud thereon;

Fig. 9 is a cross sectional view taken at 9-9 in Fig. 8 to show theconstruction and operation of this embodiment of my invention;

Fig. 10 is a cross sectional detail of the construction of a blade andone method of attaching it to the body;

Fig. 1l is a fragmentary view similar to Fig. 9 showing the operationand results of the wall smoother type View taken at 2-2 in Figof blade;and

Fig. l2 is an elevational view similar to that of Fig. 8 showing howthese blades may be attached to a body to provide helical instead ofstraight blades.

Referring now to the drawings and particularly to Figs. l to 3 thereof,the numeral 10 indicates a hollow shank adapted to be attached at itsupper end to a rotary drill stem (not shown), and provided at its lowerend with a coupling member 11 adapted to receive a bit 12. An outlet 13is formed in the bit 12 near the cutting edges thereof, and drilling uidor mud is forced downwardly through the shank 10 and escapes through theopening to wash rock cuttings and detritus upwardly, around the outsideof the shank, and to the surface so that the well is kept celan at alltimes and the bit is free to drill through the formation being cut. Thisprocedure is well known, and the drill stem (not shown), the couplingmember 11, and the bit 12 may be of any suitable type, of which thereare many known in the art.

The various drills which I have shown and described in my previouslymentioned co-pending applications rely upon the use of a hammer memberwhich is reciprocably mounted upon the shank 10, and which is adapted tobe raised and then dropped to impact against an anvil or cam by reasonof the relative rotation between the fluid drag body and the shank. Inmy previously mentioned co-pending applications, various methods aredisclosed i for transforming the relative rotation between the iiuiddrag body or retarder and the shank 10 into reciprocatory motion ofthehammer body, and one of the simplest of these methods is the form shownin Fig. 1, in which a driving cam 14 is rigidly attached to the shank10, While a driven cam 15 is adapted to override the driving cam and toimpact against the latter. The driven cam l5 may be rigidly connected toa bladed hammer body 16, and thus any rotation between the body and theshank 10 Will cause the driven cam 15 to be raised with respect to thedriving cam 14 and then dropped downwardly to impact against the latter,the weight of the hammer body adding to the force of the impact.Regardless of the type of construction or method of operation which isused, however, the various impact drills disclosed in my previouslymentioned co-pending applications rely upon a seriesof radiallyextending blades or vanes which are attached to the body 16 and extendoutwardly therefrom to engage the drilling fluid or mud as it passesupwardly around the shank 10. The drilling uid, because of itsviscosity, weightand similar characteristics, opposes the passage of theblades or vanes through the fluid, thereby acting as a drag or retardingforce which slows the rotation of the body 16 with respect to the shank10, thus effecting relative rotation between the cams.

In some cases, it may be desirable to rotate the shank 10 at arelatively high speed while keeping the rate at which the hammer impactsagainst the anvil at a ,relatively low value. If rigid blades are used,the impact rate will be increased as the speed of the shank 10 isincreased, but if resilient blades are used, there will be a tendencyfor the blades to be folded back against the surface of the rotatableblade supporting body as the speed of the latter is increased. Thisfolding back decreases the area of the blades which is directed againsta drilling uid and consequently there is a tendency to limit theretarding torque delivered to the body. In this way, the speed ofrotation of the body 16 with respect to theV shank 10 may be maintainedwithin fairly narrow limits while the rotational speed of the shankvaries between rather wide limits.

While various forms of resilient blade construction may be used, onevery satisfactory form is shown in Figs, 1 to 3 where it will be seenthat a number of individual blade sections 17 are grouped to provide aseries of longitudinally extending vanes. Each of the blade sections 17,as indicated in Fig. 3, is formed of a T-shaped member attached to thebody 16 so that the stem of the T projects radially outwardly therefrom.The cross bar or base of the T-shaped section 17 is suitably attached 1;

to the body 16, and a stiifener 20, preferably in the form of a wire orthin sheet core, is formed in the stern and the base of the bladesection to provide increased strength for the latter. From the nature ofthe conditions under which this blade section is used, it will beapparent that the section must be capable of withstanding a large amountof abrasion, moisture, grease, oil, and shearing forces which would tendto tear the stem from the base. Most of these requirements are met byone or another of the synthetic rubbers, and consequently I prefer toform the blade sections 17 of a synthetic rubber with the reinforcingmember 20 extending radially outwardly to a point considerably short ofthe end of the section. In this way, the reinforcing core 20 stiffensand strengthens the section 17 near its base, while leaving the tiprelatively unrestrained so that it may be deformed in the mannerpreviously described.

The radial distance which the stem of the blade section extends into thefluid is correlated with the size of the vell being drilled so that theblades preferably just miss the walls of the well. In this way, themaximum blade area is presented to the drilling fluid while the bladesare not worn by constant rubbing against the wall of the well. Thelength of the individual blade sections 17, measured along thelongitudinal axis of the body 16, may be of any convenient value, but ispreferably relatively short so that damage to one of the sections willnot require the replacement of more than that portion of thelongitudinally extending blade actually damaged. lt will be apparent, ofcourse, that the individual blade sections 17 may be combined intoV asingle blade (not shown) should this be thought desirable, but normallythe advantages to be gained from using the smaller sections will morethan outweigh the advantages of using the longer sections.

Under certain conditions the possibilities of damaging one or more ofthe blade sections 17 is very great, and therefore it is desirable to beable to replace damaged sections with a minimum of eifort. Consequently,I have developed the method of attachment shown in Fig. 2 where it isseen that the retarder body 16 is provided with a series oflongitudinally extending slots 21 adapted to receive the stem portion ofthe blade sections 17. These sections are inserted through the slots Z1from the interior of the body 16, with the stem portion extendingradially outwardly therefrom and with the cross bar portion bearingagainst the interior of the body. When all of the blade sections 17 havebeen inserted in the body 16, a liner 22 is placed within the body tobear against the innermost faces of the cross bars of the bladesections, holding the latter against movement and retaining them in thedesired position. if desired, spacers 23 may be placed between the body16 and the liner 22, extending between the adjacent longitudinal edgesof the blade sections so that the latter are held against any horizontalor rotational movement. In this way, a very rugged construction isprovided which will withstand the normal severe usage to which suchequipment is subjected.

It is sometimes desirable to provide helical blades or varies for thefluid drag body instead of the straight longitudinally extending biadesheretofore described and the method of mounting just described lendsitself very well to this form of construction. As indicated in Fig. 4,the desired shape of the blades may be marked upon a body 16a and aseries of slots then formed in the body.

following these lines. The blade sections 17 are then inserted throughthese slots, and the liner 22 is placed within the housing to hold thesections in this position. Spacers similar to the spacers 23 of the formshown in Fig. 2

may be used if desired, but it will be noted that these modified spacersmust be inserted between'the adiacent longitudinally extending edges ofthe stern portions with a rotary motion so that the spacers are, ineffect, screwed into the body 16a.

Where the construction of the body 16 is such to render it impracticalto forni the various slots 21 therein and insert the liner 22, it may befound desirable to attach the blades to the exterior surface of thebody. The type of blade shown in Fig. 3 may be attachedfin such a mannerby placing the cross bar portion of the section in a metal enclosurewhich may be welded, riveted or screwed onto the body 1&3. Where theblade is to be Welded to the body 16, however, the heat of the weldingoperation may damage the rubber portion of the blade, and

* thereby change its strength. To overcome this diflicuity,

I have developed the optional form of construction illustrated in Figs.5, 6 and 7 wherein a blade 17a is provided with a resilient stem portion25, similar to the stem portion of the blade section 17, and likewiseprovided Y with a Stiffening core or wire 2d. At its innermost end, thethickness of the stem portion 25 is increased and the ends of thestiiener are bent outwardly to form the cross bar of the T-shapedsection. A backing plate 26 is tackwelded or otherwise securely held tothe cross bar portions of the core 20, and clamping plates 27 and 27aare attached to the cross bar section of the stitening member on theside of the latter adjacent the stem portion 25. These clamping plates27 and 27a are thick enough to engage and securely hold the enlargedportion of the stem portion and, with the cooperating support of thestili"- ening core 20, form a rugged and secure holding member for theblade section 17a. It will be realized that the stem portion 25 may bebonded to the stilening core 20 and also to the holding plates 27 and27a, but in most instances this is not necessary.

To attach the blade sections 17a to the body 16, the sections are placedin the desired positions on the body with the backing plate 26 againstthe body and the stem portion 25 extending radially outwardly therefrom,and the cross bar portion of the blade section is then welded around itsedges to the body. A damaged blade section may be removed by applying atorch around the edges of the cross bar portion of the blade section,and a replacement section may then be welded in its place.

It will be realized that the use of the stiiening core 20 is notessential since somewhat similar results may be obtained byprogressively increasing the thickness of the stem portion of the bladesection 17 or 17a. The attaching means which may be employed with thesethicker blade sections will vary with the particular form of bladesection and whether it is surface mounted as shown in Fig. 6, or isinserted through the body 16 as shown in Fig. l. These various attachingmeans, of course, can and preferably will, be quite simple, and will beapparent to those skilled in the art.

Similarly, where the stiffening core 20 is used, its form may be variedto meet the requirements of the particular application. If relativelyshort blade sections 17 are used, similar to the type shown in Figs. 1and 4, the

individual sections may be provided with their own L separate andindependent stifening members. Individual sections designed forreplacement will, of course, be constructed in this manner and thestiiening core 20 will generally be formed as a U-shaped member with itsends bent in opposite directions, perpendicular to the plane of the U.Where a series of individual sections 17 or 17a are to be joinedtogether, or where a continuous type blade is to be used, the stilfeningcore 20 may take the form shown in perspective in Fig. 7. If this formof core is used for a series of sections, a damaged section may beremoved by merely cutting the core 20 between the adjacent sections andreleasing the cross bar portion from the body 16 in the appropriatemanner.

While the use of discontinuous blades formed of a plurality ofindividual sections found preferable because of the economy and ease ofreplacement, it is sometimes desirable to use a continuous blade tosecure some particular result. One such application is illustrated inFigs. 8 and l2, where I have illustrated how the resilient blades may beadapted to wipe the walls of the well and coat the latter with a layerof mud. The advantages of such a device will be appreciated when it isremembered that the walls, as they are cut by the drill bit, arerelatively rough and offer a great frictional resistance to the upwardflow of the drilling mud or fluid from the bottom of the well.Furthermore, where the walls are relatively porous, there is anincreased opportunity for any iiuid within the well to escape therefromand likewise for unwanted fluids to seep into the well. Consequently, itbecomes a matter of some importance to provide a coating of a smooth,relatively dense material on the walls if the maximum etciency in thedrilling of the well is to be obtained. It is to be understood, ofcourse, that the mud layer is not intended to be a replacement orsubstitute for the casing which is customarily used 17 or 17a willgenerally be n i rubber.

6 When applied as a compacted layer to the walls of the well, however,the drilling uid or mud provides a surface having the desirable featuresheretofore mentioned, with the additional advantages that by formingthis layer with my improved device about to be described, theseadvantages are obtained at a practically negligible cost.

In the form shown in Figs. 8, 9, 10 and 211, the numeral 10 indicates ashank adapted to be lowered into a well and rotated therein and thenumeral 30 indicates a generally tubular body mounted on the shank andadapted to be rotated with respect to the walls of the well. The tubularbody 30 may be the hammer body of one of my drills, and hence may berotatable with respect to the shank 10 in addition to being rotatablewith respect to the walls. However, rotation of the tubular body withrespect to the shank 10 is relatively unimportant insofar as thepresently described features are concerned, so long as the body isrotatable with respect to the walls, and thus the tubular member 30 maybe rigidly connected to the shank 10 if this is found desirable.

Mounted on the body 3i) are a series of generally radially projectingblades 31 which extend along the length of the body and are formed of aresilient material such as The construction of the blades 31 isgenerally similar to the construction of the blade sections 17 of thepreviously described forms but whereas the previously described bladeswere purposely formed short enough to clear the walls of the well, theblades 31 are made of a suiiicient length to scrape against the wallsand be turned backwardly by this movement. As indicated in Fig. l0, thetips of the blades 31 are preferably made quite thin to increase theirilexibility so that they bear against the wail with a iirm but resilientpressure. When the body is first lowered within a Well, only the tips ofthe blades 31 will bear against the wall, but later, as indicated inFig. 11, the wall will become plastered with mud and a greater portionof each of the blades will be bent rearwardly to provide a greaterwiping or trowel action. Because of the ilexibility requirements of suchblades, I have found it generally unnecessary to provide any resilientstiifening material such as the core 20 of the blade sections 17, butsuch stiifening members may be used if necessary to increase theresilience of the blades or to increase their resistance to tearing.

A cross section of a blade 31 meeting these requirements is shown inFig. 1i) wherein it is seen that the tip portion 32 is made considerablythinner than the remainder 0f the stem portion 33, while a cross-barportion 34 is formed integral with the stem 33 to provide a T-shapedsection similar to the section of the blade 17 previously described.

Generally, it is preferable to use a continuous type blade, such as thatshown in Fig. 8, instead of a discontinuous blade such as that shown inFigs. l and 4, but where the discontinuous type of blade is used, it maybe inserted through slots cut in the body 3i? and held therein in amanner similar to that shown and described in connection with Fig. l.However, where the continuous type of blade is used, the length of theslots necessary to accommodate a blade of this type is generally such asto weaken the tubular body 30 and hence I prefer to attach a continuousblade to the surface of the body in any one of several suitable manners.

As seen best in Figs. 10 and ll, one method of accomplishing this is toprovide a metal fastening strip 35 adapted to iit against the tubularbody 30, and having a pair of arms 36 and 36a adapted to lit around andengage the cross bar section 34 of the blade 31, while permitting thestem portion 33 to extend radially outwardly therefrom. The metallicholding strip 35 is preferably bonded or otherwise securely held to theblade 31 throughout the entire length of the latter, thereby providing arm support which may be readily attached to the tubular body 30 whetherthis work is done in a shop or in the field. One

in such wells.

7 of the simplest methods of rigidly attaching the strip 35 to thetubular body 30 is to weld the longitudinal edges of the strip to thebody so that a solid connection is quickly formed, while permitting thestrip to be removed by the use of a torch which is generally availablein the field.

In the operation of this device, drilling fluid or mud is forceddownwardly through theV shank 10 to a point adjacent the drilling bit,where the mud escapes from the shank and is then forced upwardly aroundthe outside of the shank, carrying with it the detritus formed at thebottom of the well. As the mud flows past the tubular body 39, theblades 31, which are rotating with respect to the wall of the well,force a portion of this mud against the wall, and the blades trowel orplaster it to form a smooth coating on the inside of the walls. As thethickness of the mud coating is increased, the blades 31 are bentrearwardly to compensate for this, and they therefore bear against thecoating with a greater pressure, thus compacting the mud and forming adenser coating. While the effective diameter of the well is decreased bythe coating of mud, the thickness of the coating is limited by theincreased pressure of the resilient blades 31 thereagainst since thispressure will tend to wipe off some of the mud if the thickness of thecoating becomes excessive. yIn this way, a sufficient area is alwaysleft for the passage of the mud upwardly through the well, while theroughness and the porosity of the walls is decreased to improve thedrilling operation.

In Fig. l2, I have illustrated an optional form of my device in whichthe tubular body 30a is provided wtih helical blades 31a, the tubularbody being mounted upon the shank 10 for rotation with respect to thewalls of the well. If the tubular body 30a is rigidly connected to theshank 10 for rotation therewith, the helical blades 31a will tend to actas a pump to lift the fluid and drive it upwardly through the well. Ifthe body 30a, on the other hand, is connected to the hammer member ofone of my rotary impact drills, the upward flow of the fluid will tendto drive the blades 31a so that they rotate with respect to the shank.The advantages to be gained from this latter form of operation arediscussed in my previously mentioned co-pending applications, and neednot be repeated here.

From the foregoing it will be seen that I have shown and described anovel retarder member for rotary impact drills which will not hang up onprojections within the well. This feature is further enhanced by the useof the Vwall wiper type of blade shown in Figs. 8 to l2, where thesmoothing of the wall and the decreasing of its porosity i aidmaterially in the efciency of the drilling operation. l"

Furthermore, these drills have a certain torque controlling or limitingfeature which can be used to great advantage in controlling the speed ofimpacting the hammer as the rotational speed of the shank 10 is changed.

While I have shown and described preferred and modified forms of myinvention, it will be apparent that changes may be made therein withoutdeparting from the spirit of the invention as defined herein and I donot wish to be restricted to the particular form or arrangement of partsherein described and shown except as limited by my claims.

I claim:

1. A drill of the class described which includes: a shank adapted to berotated in a well having drilling fluid therein; a body mounted on saidshank for rotation with respect to the wall of said well, said bodyhaving a series of generally longitudinally extending slots therein; aseries of T-shaped blades having resilient stem portions extendinggenerally radially through said slots to engage said uid, said sternportions being of suflcient stiffness to develop a torque retarding therotation of said body, and of sufficient resilience to pass over anyobstacles of a type normally encountered in wells, said blades beingprogressively circumferentially deflected as said torque developed bytheir passage through said uid is increased;

and a liner Within said body bearing against the cross-bar portions ofsaid T-shaped blades to hold said blades in place.

2. A drill of the class described which includes: a shank adapted to berotated in a well having drilling fluid therein; a body mounted in saidshank for rotation with respect to the wall of said well, said bodyhaving a series of generally longitudinally extending slots therein; aseries of longitudinally extending T-shaped blades having resilientstern portions extending generally radially through said slots to engagesaid uid, said stem portions being of suicient stiffness to develop atorque retarding the rotation of said body, and of sutlicient resilienceto pass over any obstacle of a type normally encountered in wells, andrelatively rigid means within said body bearing against the cross-barportions of said T-shaped blades to hold the latter in place.

3. A drill of the class described which includes: a shank adapted to berotated in a well having drilling fluid therein; a body mounted on saidshank for rotation with respect thereto and with respect to the wall ofsaid well, said body having a series of longitudinally extending slotstherein; a series` of T-shaped blades having relatively thin resilientstem portions extending generally radially through said slots to engagesaid uid but not said wall'of said well, said stem portion being ofsufficient stiffness to develop a torque regarding the rotation of saidbody with respect to said wall when said shank is rotated, and ofsufficient resilience to pass over any obstacle' of a type normallyencountered in wells, said blades being progressively circumferentiallydeflected as said torque developed by their passage through said iluidVis increased; and a liner within said body bearing against thecross-barportion of said T-shaped blades to hold said blades in place.

4. A drill of the class described which includes: a shank adapted to berotated in a well having drilling uid therein; a body mounted on saidshank for rotation with respect thereto and with respect to the wall ofsaid well, said body having a series of slots therein; a series' ofrubber T-shaped blades having resilient stem portions extending radiallyfrom said body to engage said iluid and adapted to bear against saidwall to make wiping contact therewith, said stem portions being ofsufficient stiffness to develop a torque opposing the rotation of saidbody with respect to said wall when said shank is rotated whereby saidbody is retarded with respect to said shank, and of sufficientresilience to pass over any obstacle of a type normally encountered inwells; and a means within said body engaging the cross-bar portions ofsaid T-shaped blades to hold the latter in place.

5. A drill of the class described which includes: a shank adapted to berotated in a well having drilling fluid therein; a body mounted on saidshank for rotation with respect thereto and with respect to the wall ofsaid well, said body having a series of slots therein; a series ofrubber T-shaped blades having relatively thin resilient stern portionsextending radially from said body to engage said fluid, said sternportions being of sufficient stiffness to'develop a torque opposing therotation of said body with respect to said wall when said shank isrotated whereby said body is retarded with respect to said shank, and ofsutiicient resilience to pass over any obstacle of a type normallyencountered in wells, said blades being progressively circumferentiallydeected as said torque developed by their passage through said iiuid isincreased;

and means within said body engaging the cross-bar portion of saidT-shaped blades to hold the latter in place.

6.v A drill of the class described which includes: a shank adapted to berotated in a well having drilling fluid therein; a body mounted on saidshank for rotation with respect thereto and with respect to the wall ofsaid well, said body having a series of longitudinally extending slotstherein; a series of T-shaped blades having resilient stem portionsextending radially through said slots to engage said Huid and to bearagainst said wall to make wiping contact therewith, said stern portionsbeing of suicient stiffness to develop a torque opposing the rotation ofsaid body with respect to said wall when said shank is rotated wherebysaid body is retarded with respect to said shank, and of sufficientresilience to pass over any obstacle of a type normally encountered inwells; and liner means within said body bearing against the cross-barportions of said T-shaped blades to hold said blades in place.

References Cited in the file of this patent UNITED STATES PATENTS SumanAug. 23, 1921 Kennedy May 22, 1934 Bettis July 25, 1939 Sandstone June27, 1944 Wright June 18, 1946 Snyder Aug. 5, 1947

